Java Stream流之求和的实现

BigDecimal bb =list.stream().map(Plan::getAmount).reduce(BigDecimal.ZERO,BigDecimal::add);

double max = list.stream().mapToDouble(User::getHeight).sum();

//todo stream流的使用

  //todo filter：过滤操作；保留符合过滤条件的对象；这是一个中间操作；后面可以带最终操作

  //todo mapToInt: 将数据根据double类型来处理；

  public static void main(String[] args) {

   List<SalesOrder> list = createSalesOrder();

   //获取集合中城市为上海的数量

   System.out.println( "mapToInt获取和:" +list.stream().filter(s -> s.getConsigneeCity().equals( "上海" ))

    .mapToInt(SalesOrder::getCreateUserId).sum());

   //利用stream流中的函数获取相关数值信息

   IntSummaryStatistics summaryStatistics = list.stream().filter(s -> s.getConsigneeCity().equals( "上海" ))

    .mapToInt(SalesOrder::getCreateUserId).summaryStatistics();

   System.out.println( "summaryStatistics函数获取数量:" +summaryStatistics.getCount());

   System.out.println( "summaryStatistics函数获取平均值:" +summaryStatistics.getAverage());

   System.out.println( "summaryStatistics函数获取最大值:" +summaryStatistics.getMax());

   System.out.println( "summaryStatistics函数获取最小值:" +summaryStatistics.getMin());

   System.out.println( "summaryStatistics函数获取和" +summaryStatistics.getSum());

  }

static List<SalesOrder> createSalesOrder(){

   List<SalesOrder> list = new LinkedList<>();

   SalesOrder salesOrder = new SalesOrder();

   salesOrder.setCreateUserId( 12 );

   salesOrder.setConsigneeCity( "上海" );

   list.add(salesOrder);

   salesOrder = new SalesOrder();

   salesOrder.setConsigneeCity( "上海" );

   salesOrder.setCreateUserId( 24 );

   list.add(salesOrder);

   salesOrder = new SalesOrder();

   salesOrder.setConsigneeCity( "北京" );

   salesOrder.setCreateUserId( 18 );

   list.add(salesOrder);

   salesOrder = new SalesOrder();

   salesOrder.setConsigneeCity( "深圳" );

   salesOrder.setCreateUserId( 16 );

   list.add(salesOrder);

   salesOrder = new SalesOrder();

   salesOrder.setConsigneeCity( "广州" );

   salesOrder.setCreateUserId( 30 );

   list.add(salesOrder);

   salesOrder = new SalesOrder();

   salesOrder.setConsigneeCity( "杭州" );

   salesOrder.setCreateUserId( 40 );

   list.add(salesOrder);

   return list;

  }